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Getting your five a day? Don't get too comfortable - there is now a host of recommended daily and weekly prescriptions to follow for better health, covering everything from sleep to sunshine. The latest came from researchers at Cambridge University, who studied the effects of work on mental health and life satisfaction, and concluded eight hours of work a week is the key to wellbeing. That followed a finding from the University of Exeter, based on interviews with 20,000 people, that we should all be aiming for a two hour "dose" of nature every week.

Psychologist Linda Blair says thenew trend for quantitative guidelines stems from a need for simple rules to govern our increasingly hectic lifestyles - along with the arrival of technology that allows us to log and count every detail of our day.

"We are so busy, and we want to be looked after - we want quick answers," she says. "Perhaps these quotas have a place as a general parameter, but the key to wellbeing is listening in, rather than measuring out. No two days will be alike - that's what makes life so much fun - and rather than measuring and comparing ourselves to external standards, it's better to listen to yourself and learn to respond to what you need each day."

Snappy as they sound, the effect of these guidelines on our behaviour is also unclear. "In principle it's of course a good idea to make clear what a healthy diet is, but the five a day message, for example, hasn't produced any marked change in consumption of fruit and vegetables," says Jack Winkler, emeritus professor of nutrition policy at London Metropolitan University. "Those who are interested in nutritional advice, and absorb it, are in the minority."

So how accurate - not to mention realistic - are the formula being thrown our way, and are they really making us any healthier?

8 hours of sleep

Sleep has become a national obsession, with a slew of apps, trackers and gurus telling us we need eight hours a night. But don't fret if you're getting - and needing - more or less than that. "We have no idea where that figure came from," says Neil Stanley, a sleep expert and author of How To Sleep Well. "There isn't a shred of proof we need it." One possible explanation is the 8-hour day movement, which started in Australia, Britain and America in 1850, and was based around the idea that the working man needed 8 hours of work, 8 hours of leisure and 8 hours of sleep within a 24-hour period.

"It's not a bad figure to aim for, but sleep is like height," says Stanley. "It's genetically determined and we're all different. There are short sleepers, who feel fine after four hours, and long sleepers, who need nine hours. So sleep trackers are quite pointless because they're measuring something that's as individual as a fingerprint." Last month, neurologist and sleep disorder specialist Dr Guy Leschziner warned sleep-tracking apps were making people so anxious about getting enough sleep they were developing insomnia.

It's simple to work out how many hours you need, says Stanley. "How do you feel at 11am each day? If you feel OK, then you're getting enough sleep. If you feel like you could put your head down on your desk and fall asleep right there, you're not getting enough. So ignore the 8-hour-rule. It doesn't matter how long it takes you to fall asleep, how many times you wake in the night, or how you feel when you wake up. What matters is how you feel at 11am."

10,000 steps

An entire industry has been built upon the belief we should be taking 10,000 steps a day. The figure originates from a Japanese marketing campaign from the 1960s, seeking to capitalise on the 1964 Tokyo Olympics with one of the world's first fitness trackers.

Last year, however, Public Health England chiefs denounced the 10,000 figure, and a recent study from Harvard University found taking as few as 4,400 steps per day led to a 41 per cent reduction in mortality. The government instead advises that adults aged 19 to 64 should try to get 150 minutes of moderate activity, or 75 minutes of vigorous activity, every week.

"The 10k figure is arbitrary," says personal trainer Matt Roberts. "It isn't based on scientific research, and it doesn't take into account intensity. You can have somebody who shuffles around all day and hits the target, versus somebody who regularly does short bursts of intense workouts that don't clock up many steps. With exercise, quantity isn't everything. "The number I tell my clients to aim for is four: this is the number of days each week you should be exercising to the point you feel out of breath and sweaty. A jog, a brisk walk that leaves you red faced, a bike ride or a HIIT class will suffice."

Of course, clocking up 10,000 or more steps a day is no bad thing, he says. "But what should concern you is when you last built up a sweat." Last year, the World Health Organisation reported that a third of adults in the UK are not getting enough exercise and that activity levels had shown little improvement between 2001 and 2016.

An entire industry has been built upon the belief we should be taking 10,000 steps a day. Photo / 123RF

5 portions of fruit and vegetables

This now ubiquitous formula, launched by the UK government in 2003 in a bid to make healthy eating easier, has been embraced by the food industry, with supermarkets filled with labels helping you to count and reach your five a day. "It's from the World Health Organisation," says Helen Bond, "which recommends 400g of fruit and vegetables each day for wellbeing, after several major studies found this helps in major disease prevention, including heart disease and certain cancers. It's the minimum we should be eating, not the upper limit to aim for."

Indeed, research published in 2017 by Imperial College London prompted some to say the ideal intake should be ten portions of fruit and veg, or 800g a day. Unfortunately, though, most of us don't even manage five: just 8 per cent of teenagers get their five-a-day, while 31 per cent of adults aged 19 to 54 do, and 26 per cent of over 65s.

Debate continues, too, over what should count as a portion. Some experts now say half of our daily portions should come from green veg. A small glass of fruit juice still counts as one of your five a day under government recommendations, but there have been calls to exclude it because of its high sugar content, and to encourage people to eat whole fruit instead.

Debate continues over what should make up your five-a-day. Photo / 123RF

8 glasses of water

"The government says we need six to eight glasses of water each day (around 1.9litres) to stay healthy," says dietitian Helen Bond. "But how much we really need varies on our age, gender, the weather, and how active we are." There is currently no safe upper limit for water, although excessive amounts can cause water intoxication. "Forget eight glasses, urine colour and thirst are the only indicators to think about," says Bond. "If you're drinking enough water your urine will be the colour of pale straw. If it's darker, drink more. If you're thirsty, drink more. And all fluid counts, apart from alcohol. Even things like coffee, tea and juice, although plain water is healthiest."

We're advised to drink around six to eight glasses of water each day. Photo / 123RF